Behaviour of polymer dispersed cholesteric droplets with negative dielectric anisotropy in electric fields

Abstract

The behaviour of chiral, polymer dispersed cholesteric liquid crystals with negative dielectric anisotropy in electric fields has been studied for a system with large cholesteric pitch (several μm) using polarizing microscopy. A uniformly oriented region appears in the centre of the droplets for voltages above a threshold voltage. We find that the radius of this region increases exponentially with increasing field strength, while the threshold voltage decreases with increasing drop diameter and with increasing pitch. Investigation of the dynamics reveals a single step mechanism with a time constant of a few seconds when a field is suddenly switched on. The switch-off process is more complex and much slower.